The invention relates to a method and apparatus for qualitative or quantitative noninvasive assessment of the metabolic and structural components of skin and nearby tissues using Raman spectroscopy. The invention relates to maintaining depth and position of focus of a Raman excitation source, regardless of whether an imaging light collection system is used. This system also provides first order servo correction for automatic focusing of an imaging system. The invention additionally relates to identifying spectroscopic depth markers in tissues, and to detecting skin abnormalities and assessing the aging of skin and related tissues.
There has always been a need for reliable and precise quantitative methods and associated apparatus for diagnosing medical abnormalities and for assessing the general condition of body tissues. While any approach that offers early and reliable warning of medical problems has some utility, noninvasive methods offer many advantages. Anticipation by a patient of pain and scarring associated with invasive procedures can cause delays in seeking medical attention. There is also a myriad of inconveniences, risks and difficulties associated with direct collection and contact with patient body fluids. For these reasons, there has been intense scientific and engineering research into devising noninvasive approaches to assessment and diagnosis of medical conditions.
Use of spectroscopic methods, while of considerable use in direct in vitro application to fluids, has not found equal in vivo application. In vivo sampling is substantially more complicated for a variety of reasons, although some of the challenges can be handled by reference to in vitro procedures. First, even in vitro procedures require at least some sample preparation before spectroscopic interrogation. But in vivo samples cannot be handled with nearly the ease of in vitro samples. All chemometric analyses benefit from the availability of samples having known composition of various analytes. Selectively modulated in vitro samples are much easier to synthesize or otherwise obtain than in vivo samples. Thus, samples for chemometric interpretation of in vivo samples can be expected to require specialized approaches to sample preparation and specifically designed methods for obtaining modulated samples of known composition. Long data collection times are needed to extract small signals from some samples, but in vivo sampling requires the patient to endure the waiting. Prolonged data collection is not always practical. Moreover, applying too much excitation light to in vivo samples can lead to catastrophic results.
Noninvasive in vivo chemical analysis of human and animal tissues has long been a goal of chemists and the medical community. Blood oximetry is an example of a noninvasive form of analysis that is now ubiquitous in intensive care and other situations. Noninvasive techniques involve contacting the tissue in question with some form of electromagnetic radiation, and detecting the effect of the contact on the radiation. The frequency range of the radiation and the choice of tissue to contact, determines the type of structural, concentration or other physico-chemical information that is available.
The optics of human skin have been extensively reviewed. The interaction with visible light contacting blood in the capillary beds just beneath the epidermis of human skin can be exploited to estimate the oxygen content of blood, thereby giving a quantitative measure of the condition of the patient""s respiratory and cardiovascular systems, i.e. blood oximetry. The present invention is directed to assessing the condition of the skin at the molecular and supramolecular scale, making vibrational spectroscopy an ideal probe.
The invention provides a method and apparatus for obtaining feedback to drive a servo system for aligning and maintaining alignment in optical systems that bring light to an in vivo skin sample, for adjusting the focus of the optical system, for adjusting the net depth of focus of the optical system within the in vivo system under characterization, and for driving a tissue-directed search and mapping algorithm. The invention additionally provides a method and apparatus for obtaining feedback to drive a servo system for aligning and maintaining alignment in optical systems that collect light from an in vivo skin sample, and for adjusting the focus of the optical system. These methods comprise adjusting the angle of incidence of electromagnetic radiation and/or providing a shielding lens to block scattered incident light, or otherwise limiting the field of view of the Raman scattered radiation collection system to exclude optical surfaces of the excitation delivery portion of the optical system.
Also provided is a method and apparatus for identifying spectroscopic depth markers in tissues. In one embodiment, the method comprises discriminating between Raman signals originating on outer portions of skin from signals originating from substances deeper within the skin or other tissues. In some embodiments, these methods comprise selecting optics for Raman detection to maximize one or more Raman features corresponding to lipids and proteins of the skin.
The invention provides a method and apparatus for obtaining spectroscopic information from living tissue of a subject. In one embodiment, the method comprises irradiating a tissue of interest in a subject with light having an excitation wavelength and that passes from a light source through a first adjustable lens, and passing spectra that are emitted by the tissue through a second adjustable lens. The spectra that are passed through the second adjustable lens are then collected and analyzed to determine a target signal associated with an analyte of interest. The method further comprises deriving a correction signal from the target signal, and adjusting the position of the first adjustable lens or the second adjustable lens on the basis of the correction signal so as to enhance the target signal. In a preferred embodiment, the spectra are Raman spectra. The method can optionally further comprise selectively dispersing a target wavelength of the collected spectra prior to analyzing the collected spectra. Preferably, the dispersing comprises filtering out wavelengths other than the target wavelength, or passing the collected spectra through a spectrograph.
In another aspect, the invention provides a non-invasive method and apparatus for spectroscopically probing and mapping a target layer of skin in a subject. The method comprises irradiating a target layer of skin in a subject with light having an excitation wavelength that passes from a light source through a first adjustable lens, passing spectra that are emitted by the tissue through a second adjustable lens, and collecting spectra that are passed through the second adjustable lens. The method further comprises analyzing the collected spectra to determine a target signal associated with the target layer of skin, and adjusting the position of the first adjustable lens or the second adjustable lens so as to increase the target signal. Optionally, the method further comprises deriving a correction signal from the target signal and relaying the correction signal to the first adjustable lens or to the second adjustable lens, wherein the correction signal effects an adjustment of the first adjustable lens or the second adjustable lens. In one embodiment, the method and apparatus include an adjustable aperture, such as one or more irises, as in a confocal microscope, positioned between the skin and the light collection system. A correction signal derived from the target signal is then used as feedback to the adjustable aperture to optimize the collection of spectra from the target layer of skin.
In another aspect, the invention provides a method and apparatus for spatial mapping and detecting abnormalities in living tissue of a subject. The method comprises irradiating a tissue of interest in a subject with light having an excitation wavelength and that passes from a light source through a first adjustable lens, passing spectra that are emitted by the tissue through a second adjustable lens, and collecting spectra that are passed through the second adjustable lens. The method further comprises analyzing the collected spectra to determine a target signal associated with a tissue feature indicative of an abnormality, deriving a correction signal from the target signal, and adjusting the position of the first adjustable lens or the second adjustable lens on the basis of the correction signal so as to enhance the target signal. In one embodiment, the tissue of interest comprises skin. Other examples of tissues of interest include, but are not limited to, stratum corneum, epidermis, intradermal capillary beds, and dermis.
The invention further provides a method and apparatus for stabilizing a wavelength and/or amplitude of light emitted by a diode laser. The method comprises irradiating a specimen with excitation light from the diode laser, and collecting Raman spectra at a target wavelength emitted by the irradiated specimen, wherein the target wavelength is associated with a strong feature in the specimen. In one embodiment, the target wavelength is associated with silica, as present in the optical path, such that an optical element within the system serves as the irradiated specimen. The target wavelength associated with silica is a wavenumber shift of about 1003 cmxe2x88x921 from the excitation wavelength. The method further comprises determining a quantity of spectra emitted at the target wavelength, relaying to the diode laser a signal proportional to the determined quantity, and regulating the temperature of the diode laser so as to maintain a maximal spectra emitted at the target wavelength.
In another embodiment, Raman spectra are collected at two or more wavelengths: at least one positive target wavelength associated with a strong feature in the specimen, and at least one a negative target wavelength associated with a weak feature in the specimen. The method further comprises determining a quantitative difference between the spectra emitted at the positive target wavelength and the spectra emitted at the negative target wavelength, relaying to the diode laser a signal proportional to the determined difference, and regulating the temperature of the diode laser so as to maintain a maximal difference between the spectra emitted at the positive target wavelength and the spectra emitted at the negative target wavelength. In a preferred embodiment, the specimen is skin, the positive target wavelength is a wavenumber shift of about 2940 or 1665 cmxe2x88x921 from the excitation wavelength and the negative target wavelength is a wavenumber shift of about 2800 or 1775 cmxe2x88x921, respectively, from the excitation wavelength.
The method can be performed non-invasively on living tissue. Optionally, the method further comprises adjusting the position of a first adjustable lens located in the optical path of the excitation light so as to increase the determined quantity of the spectra emitted at the target wavelength, or the difference between the spectra emitted at the positive target wavelength and the spectra emitted at the negative target wavelength, and/or likewise adjusting the position of a second adjustable lens located in the optical path of the emitted spectra so as to increase the determined quantity of spectra or difference between the spectra emitted at the positive target wavelength and the spectra emitted at the negative target wavelength.
In another embodiment, the invention provides a method and apparatus for assessing the aging of skin and related tissues. The method comprises characterizing the content of the skin using Raman spectroscopy as described above. The aging of skin is related to morphological changes in the tissues on a spatial scale of 10-10,000 microns which can be mapped at very early stages of their development using the method of this invention. These morphological changes, i.e. wrinkles, may or may not be associated with chemical variations. These changes are purely physical and may be precisely mapped using the method of the invention. In one embodiment, the collagen, elastin, and/or keratin content of the skin is characterized. In another embodiment, the size and location of fat deposits is characterized.
In another aspect, the invention provides an apparatus for enhancing spectroscopic information obtained from living tissue of a subject. The apparatus comprises a signal analyzer adapted to receive input from a detector and a processor connected to the signal analyzer, wherein the processor is capable of producing an output signal that is proportional to a quantity of Raman spectra received by the signal analyzer from the detector. The output signal can be directed to a diode laser for regulating the temperature of the diode laser, thereby stabilizing the wavelength and/or amplitude of light emitted by the diode laser and focused onto the living tissue to be spectroscopically probed. The output signal can also be directed to an adjustable lens, either a first adjustable lens used to focus the light onto the living tissue, or a second adjustable lens used to collect Raman spectra scattered by the living tissue.
Alternatively, the output signal can be directed to an adjustable aperture, such as an iris in a confocal microscope. The adjustable aperture can be coupled to an electronically controlled translation stage that is connected to the processor and optically aligned with an input path to the detector, wherein the output signal regulates movement or diameter of the adjustable aperture along or perpendicular to an optical axis aligned with the input path of the detector. The apparatus provides a feedback system for optimizing the quality and the focusing of the spectroscopic system, and provides connections between data processors and translation stages that control the positions of optical elements in a device.